The new Third Generation Partnership Project (3GPP) standard known as Long Term Evolution (LTE) (3GPP LTE Rel-10) supports heterogeneous networks. In heterogeneous networks, a mixture of cells of different size and overlapping coverage areas are deployed. For example, a heterogeneous network may deploy pico cells served by relatively low power nodes within the coverage area of a macro cell served by relatively high power base stations. Heterogeneous networks could also deploy relatively low-power home base stations and relays to provide improved service in indoor areas. The aim of deploying low power nodes, such as pico base stations, home base stations, and relays, within a macro cell where coverage is provided by a high power base station, is to improve system capacity by means of cell splitting gains as well as to provide users with wide area experience of very high speed data access throughout the network. Heterogeneous deployment schemes represent one alternative to deployment of denser networks of macro cells and are particularly effective to cover traffic hotspots, i.e. small geographical areas with high user densities served by lower power nodes.
In heterogeneous networks, there may be a large disparity in output power of the low power nodes compared to the base stations serving macro cells. For example, the output power of the base stations in the macro cells may be in the order of 46 dBm while the output power of the low power nodes in the pico cells may be less than 30 dBm. In Release 8 and 9 of the LTE standard, a mobile terminal is required to find and perform signal measurements for cells with a Es/lot ratio greater than or equal to −6 dB. Thus, there is no requirement that the mobile terminal finds and reports pico cells in some heterogeneous deployment scenarios. Further, the large difference in output power of the macro cells compared to the pico cells may make measurements of signals transmitted by the pico cells difficult.
Therefore there is a need for a method and apparatus enabling mobile terminals operating in heterogeneous networks detect and measure signal transmitted by pico cells that could be up to 10-15 dB below the signals transmitted by overlapping macro cell base stations.